Implanted cardiac pacemakers are used to detect abnormal heart rhythms and apply electrical shocks to the heart to keep the heart beating at a desired pace. They have typically been implanted with the leads attached to the right side of the heart (due to ease of placement), but bi-ventricular pacing has recently been developed to provide better pacing efficiency, heart output and patient quality of life. In bi-ventricular pacing, one lead is placed in electrical contact with the right ventricle, and a second lead is placed in electrical contact with the left ventricle. These leads are embedded into the heart, and their placement may be achieved surgically (for epicardial placement) and percutaneously (mostly through the right side of the heart and the venous system). Bi-ventricular pacing leads include one that is placed through the venous system through the coronary sinus into a vein that is outside of the left ventricle (still epicardial, but placed in a vein).
Access the coronary sinus is quite difficult. The prior art method of placing the second pacemaker lead into the left side of the heart entails placing a guide wire or electrophysiology catheter percutaneously into the coronary sinus, then placing a guide catheter over the guide wire or EP catheter into the coronary sinus. Once the distal tip of the guide is seated in the coronary sinus, the EP catheter is removed. Then, a balloon occlusion/infusion catheter is inserted into the guide and into the coronary sinus. The balloon infusion catheter is used with a guide wire to sub-select venous branches. Venograms are done to image the venous system of the heart under fluoroscopy. The balloon on the infusion catheter is inflated during the venograms to prevent the contrast fluid (which can be infused through either the guide or the infusion catheter) from being carried out of the venous system too quickly by the normal venous flow (the contrast agent used for the venogram is injected against the flow of blood in the coronary sinus). After the venogram, the balloon is deflated. When the desired location for the lead is identified (it may be one of several coronary veins, of a site within the coronary sinus itself), the balloon infusion catheter is removed and discarded, leaving the guide catheter in place within the coronary sinus.
To place the lead, which includes an implantable tip and 20 to 25 inches of lead wire, the lead in inserted into the guide catheter and advanced to the implantation site. The leads may be tracked over a guide wire (over the wire or monorail systems are used), or pushed over a stylet. The guide wire or styletted lead is inserted through the guide and manipulated to the vein chosen for placement. Additionally, injection of contrast agent may help to visualize the venous system during placement, but the balloon catheter is no longer present to prevent the contrast agent from being quickly flushed from the site of interest.
Once the lead is in place and has been electrically tested, the doctor does not want to disturb it. The guide sheath must be removed from the body, which entails dragging it over the pacemaker lead, and this imparts force on the pacemaker lead which may dislodge the tip from its implantation site. Thus the guide catheter may be provided in a slittable or tear-away form, so that the length of pacemaker lead subject to the dragging forces of the guide catheter is minimized. The doctor maintains control of the proximal end of the lead and pulls or peels the sheath/guide while he is withdrawing it from the body over the lead. When finished, the lead gets connected to a defibrillator/pacemaker that is implanted in a pocket under the patient's skin.